Reciprocating Compressor

ABSTRACT

A reciprocating compressor includes a piston which compresses air by, while rocking, reciprocatingly moving in a cylinder and a sealing member which is fitted in a groove formed on the piston for sealing between the cylinder and the piston. In the reciprocating compressor: the sealing member has a bottom portion to be fitted in the groove formed on the piston and a side portion provided radially outwardly of the piston; and the side portion includes a bent portion so as to reduce a gap between an upper end portion thereof and the piston.

BACKGROUND

The present invention relates to a reciprocating compressor.

A background technique in the present technical field is disclosed, forexample, in Japanese Unexamined Patent Application Publication No.2011-12603. In the patent literature, a multi-stage compressor isdisclosed which includes a rocking piston provided with a lip ringhaving an upper sealing portion and a lower sealing portion with theformer being more susceptible to elastic deformation than the latter.

SUMMARY

The upper sealing portion of the lip ring disclosed in theabove-mentioned patent literature is designed to be easily elasticallydeformable, so that it tends to be excessively deformed to increase thestress applied to a curved portion of the lip ring. Furthermore, since alarge gap is formed between the upper sealing portion of the lip ringand the piston when the piston tilts relative to the cylinder, the lipring is pressed against the inner peripheral surface of the cylindercausing the stress applied to the curved portion of the lip ring to befurther increased. Therefore, the life of the lip ring cannot belengthened.

The present invention has been made in view of the above problem, and itis an object of the present invention to provide a reciprocatingcompressor in which the stress applied to the lip ring is reduced so asto lengthen the life of the lip ring.

To address the above problem, the present invention provides areciprocating compressor having a piston which compresses air by, whilerocking, reciprocatingly moving in a cylinder and a sealing member whichis fitted in a groove formed on the piston for sealing between thecylinder and the piston. In the reciprocating compressor: the sealingmember has a bottom portion to be fitted in the groove formed on thepiston and a side portion provided radially outwardly of the piston; andthe side portion includes a bent portion so as to reduce a gap betweenan upper end portion thereof and the piston.

The reciprocating compressor according to the present invention canreduce the stress applied to the lip ring used therein and can therebylengthen the life of the lip ring.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view of the main body of a reciprocatingcompressor according to a first embodiment of the present embodiment;

FIG. 2 shows sectional views of a piston and a cylinder according to thefirst embodiment of the present invention;

FIG. 3A shows a sectional view of a lip ring according to the firstembodiment of the present invention;

FIG. 3B shows sectional views of the lip ring according to the firstembodiment of the present invention;

FIG. 4 shows sectional views of a lip ring according to a first examplecase for comparison with the present invention;

FIG. 5 shows sectional views of the lip ring in a rocking stateaccording to the first example case for comparison with the presentinvention;

FIG. 6 shows sectional views of the lip ring in a rocking stateaccording to a second example case for comparison with the presentinvention;

FIG. 7 shows sectional views of the lip ring in a rocking stateaccording to the second example case for comparison with the presentinvention;

FIG. 8 shows a sectional view of a lip ring according to a secondembodiment of the present invention;

FIG. 9 shows a sectional view of a lip ring according to a thirdembodiment of the present invention; and

FIG. 10 shows a sectional view of a lip ring according to the thirdembodiment of the present invention.

DETAILED DESCRIPTION First Embodiment

A reciprocating compressor according to a first embodiment of thepresent invention will be described below with reference to FIG. 1 toFIGS. 3A and 3B.

FIG. 1 is a sectional view of the main body of the reciprocatingcompressor according to the present embodiment.

A crankcase 1 of the reciprocating compressor is for forming an internalcrank chamber 2. The crankcase 1 is broadly comprised of a cylindricalcase section 1A having a horizontal axis and a cylinder mounting seat 1Bprovided on the upper side of the cylindrical case section 1A. In thecrank chamber 2 included in the crankcase 1, a crankshaft 5 is rotatablysupported. The crankshaft 5 is integrally provided with a balance weight6. The crankshaft 5 is connected to an output shaft 4 of an electricmotor 3 and is driven by the electric motor to rotate eccentrically.

A cylinder 7 is mounted on the cylinder mounting seat 1B included in thecrankcase 1. An inner peripheral surface 7A of the cylinder 7 serves asa sliding surface for a lip ring 22 being described later. A cylinderhead 8 is mounted on the top side of the cylinder 7. A discharge chamber10 for discharging compressed air is formed in the cylinder head 8.

A piston rod 14 is, at its base end, rotatably connected to thecrankshaft 5 via a bearing 15. When the crankshaft 5 driven by theelectric motor 3 eccentrically rotates, a piston 16 provided at an endportion of the piston rod 14 reciprocatingly moves while rocking in thecylinder 7 as shown in FIG. 2. In the cylinder 7, a compression chamber17 is formed between the piston 16 and a valve seat plate 11. The piston16 includes a piston main part 18, a retainer 19, and a ring receivinggroove 21.

The piston main part 18 is integrally connected, at an underside centralportion thereof, with an end portion of the piston rod 14. The retainer19 is detachably attached to the upper side of the piston main part 18so that it can hold the lip ring 22 between itself and the piston mainpart 18.

The lip ring 22 fitted on the outer circumferential side of the pistonmain part 18 is a sealing member for sealing between the piston 16 andthe cylinder 7 so as to prevent air (pressure) leakage from thecompression chamber 17. The lip ring 22 is made of, for example, anabrasion-resistant, self-lubricating resin material and has an L-shapedcross-section.

The lip ring 22 of the present embodiment will be described withreference to FIGS. 3A and 3B. FIG. 3A is a sectional view of the lipring 22 without any pressure applied thereto. FIG. 3B is a sectionalview of the lip ring 22 subjected to a pressure with the piston 16 in atilted state. The lip ring 22 has an annular shape and includes a bottomportion 22A to be fitted in a groove on the piston 16 and a side portion22B formed radially outwardly of the piston 16. The side portion 22Bopens wider upwardly, i.e. toward the compression chamber 17 andslidingly contacts the inner peripheral surface 7A of the cylinder 7 forsealing between the cylinder 7 and the piston 16.

According to the present embodiment, the side portion 22B of the lipring 22 has a top end portion 22B1, a base end portion 22B2, and a bentportion 22B3. The top end portion 22B1 is positioned on the upper endside of the side portion 22B. The base end portion 22B2 is positioned onthe base end side (lower end side) of the side portion 22B and extendsfrom the bottom portion 22A radially outwardly and diagonally upwardlyof the piston 16 to be connected to the top end portion 22B1 via thebent portion 22B3. The bent portion 22B3 is positioned between the topend portion 22131 and the base end portion 22B2. The side portion 22B ofthe lip ring 22 includes plural bends (i.e. a flat surface is bent atplural angles or, in the case of a curved surface, its tangential angleis discontinuously changed).

An angle θ1 formed between the top end portion 22B1 and the axialdirection of the piston 16 is smaller than an angle θ2 formed betweenthe base end portion 22B2 and the axial direction of the piston 16.Namely, with the bent portion 22B3 formed, the gap between the top endportion 22B1 of the side portion 22B and the piston 16 is narrower thanin cases where the bent portion 22B3 is not formed. This reducesdeformation of the lip ring 22 caused when the piston 16 is tilted andpressed against the inner peripheral surface 7A of the cylinder 7, sothat the stress applied to the lip ring 22 is reduced. In FIG. 3B, themagnitude of stress applied to the lip ring 22 is represented by thedegree of shading. In FIG. 3B, compared with FIG. 5, there is almost nodark shading in portions expected to be subjected to stressconcentration of the lip ring 22, indicating that the stress applied tothe lip ring 22 is reduced.

Increasing the angle θ2 formed between the base end portion 22B2 and theaxial direction of the piston 16 allows the base end portion 22B2 to betilted more toward the radial direction of the piston 16 so as to causethe top end portion 22B1 to contact the inner peripheral surface 7A ofthe cylinder 7 at a location farther from the piston 16. In this way, agap S between where the lip ring 22 and the inner peripheral surface 7Aof the cylinder 7 contact each other and the piston 16 can be widened asshown in FIG. 3B, so that the inner peripheral surface 7A of thecylinder 7 and the piston 16 can be prevented from contacting eachother.

The angle θ2 formed between the base end portion 22B2 and the axialdirection of the piston 16 is larger than the rocking angle θ (the angleformed between the axial direction of the piston 16 in a state mosttilted relative to the cylinder 7 and the inner peripheral surface 7A ofthe cylinder 7). In this way, even when the piston 16 is most tiltedrelative to the cylinder 7, the base end portion 22B2 can move radiallyoutwardly of the piston 16 allowing the contact between the lip ring 22and the inner peripheral surface 7A of the cylinder 7 to be radiallyoutside the base end portion 22B2. Thus, the gap S can be adequatelysecured between where the lip ring 22 and the inner peripheral surface7A of the cylinder 7 contact each other and the piston 16. In this way,even when the piston 16 is most tilted relative to the cylinder 7, theinner peripheral surface 7A of the cylinder 7 and the piston 16 areprevented from contacting each other.

As shown in FIG. 3A, when the lip ring 22 is subjected to no pressure,the lower end (bottom) of the lip ring 22 does not project outwardlyfrom the piston 16. This reduces the outward projection of the lower end(bottom) of the lip ring 22 from the piston 16 in a state with apressure applied to the lip ring 22. In this arrangement, the stressgenerated when the piston 16 bites into the lower end (bottom) of thelip ring 22 is reduced.

FIGS. 4 and 5 show enlarged sectional views of the lip ring 22 used in afirst example case for comparison with the present embodiment. In thefirst example case for comparison, the side portion 22B of the lip ring22 has a curved surface of a uniform curvature without any angled bend.With the side portion 228 having a curved surface of a uniformcurvature, when the piston 16 rocks, the side portion 22B of the lipring 22 is largely deformed as shown in FIG. 5 causing the bottomportion 22A and the side portion 22B to be subjected to a large stress.In FIG. 5, the magnitude of stress applied to the lip ring 22 isrepresented by the degree of shading. In FIG. 5 compared with FIG. 3B,large portions of the lip ring 22 are darkly shaded indicating stressconcentration between the bottom portion 22A and the side portion 22B.

FIGS. 6 and 7 show sectional views of the lip ring 22 used in a secondexample case for comparison with the present embodiment. In the secondexample case, the lip ring 22 is formed to have an L-shaped section. Inthe second example case with the side portion 22B being flat-surfaced,deformation of the lip ring 22 caused by rocking of the piston 16 issmaller than in the first example case, so that the stress applied tothe bottom portion 22A and side portion 22B is also smaller than in thefirst example case.

Referring to FIG. 6, a gap S between where the lip ring 22 and the innerperipheral surface 7A of the cylinder 7 contact each other and thepiston 16 is adequately secured so as to prevent the inner peripheralsurface 7A of the cylinder 7 and the piston 16 from contacting eachother. In this case, when the lip ring 22 is subjected to no pressure,the lower end (bottom) of the lip ring 22 projects outwardly from thepiston 16. This increases the outward projection of the lower end(bottom) of the lip ring 22 from the piston 16 when a pressure isapplied to the lip ring 22. In this arrangement, the stress applied tothe bottom portion 22A of the lip ring 22 when the piston 16 bites intothe lower end (bottom) of the lip ring 22 cannot be reduced.

Referring to FIG. 7, when the lip ring 22 is subjected to no pressure,the lower end (bottom) of the lip ring 22 does not project outwardlyfrom the piston 16. This is to reduce the stress generated when thepiston 16 bites into the lower end (bottom) of the lip ring 22. In thiscase, however, a gap S between where the lip ring 22 and the innerperipheral surface 7A of the cylinder 7 contact each other and thepiston 16 cannot be adequately secured.

Thickening the upper end side of the side portion 22B of the lip ring 22makes it possible to reduce the stress applied to the lip ring 22 andprevent the inner peripheral surface 7A of the cylinder 7 and the piston16 from contacting each other. Doing so, however, excessively increasesthe rigidity of the upper end side of the side portion 22B. This makesit less easy for the lip ring 22 to open wider upwardly for enhancedsealing.

As described above, according to the present embodiment, the sideportion 22B of the lip ring 22 has the top end portion 2231, the baseend portion 22B2, and the bent portion 22B3, and the gap between theside portion 22B and the piston 16 is smaller on the upper end side ofthe side portion 22B. In this way, the stress applied to the lip ring 22is reduced. Also, the gap S between where the lip ring 22 and the innerperipheral surface 7A of the cylinder 7 contact each other and thepiston 16 can be widened, so that the inner peripheral surface 7A of thecylinder 7 and the piston 16 can be prevented from contacting eachother. Furthermore, in this arrangement, the upper end side of the sideportion 22B of the lip ring 22 does not become too rigid, so that thelip ring 22 can retain adequate sealing performance. This lengthens thelife of the lip ring 22 making it possible to provide a reciprocatingcompressor which can maintain high reliability for a long period oftime.

Second Embodiment

A reciprocating compressor according to a second embodiment of thepresent invention will be described with reference to FIG. 8. Partsidentical to those described above in connection with the firstembodiment will be denoted by identical reference numerals as used aboveand their description will be omitted.

In the second embodiment, the top end portion 22B1 of the side portion22B of the lip ring 22 includes plural bends. As shown in FIG. 8, anangle θ1 formed between the top end portion 22B1 and the axial directionof the piston 16 is smaller than an angle θ2 also formed between the topend portion 22B1 and the axial direction of the piston 16. Namely, theangle formed on the upper end side of the top end portion 22131 issmaller than the angle formed on the base end side of the top endportion 22B1. In the second embodiment, too, like in the firstembodiment, the angles θ1 and θ2 formed between the top end portion 22B1and the axial direction of the piston 16 are smaller than an angle θ3formed between the base end portion 22B2 and the axial direction of thepiston 16.

In the present embodiment, with the top end portion 22B1 includingplural bends, the top end portion 22E1 extends more closely along theaxial direction of the piston 16 on the upper end side than on the baseend side. This prevents the gap between the upper end side of the sideportion 22B of the lip ring 22 and the piston 16 from becoming too wide.In this way, the stress applied to the lip ring 22 is further reducedcompared with the first embodiment. Also compared with the firstembodiment, the side portion 22B of the lip ring 22 and the innerperipheral surface 7A of the cylinder 7 contact each other at a locationradially more outward from the piston 16, so that the inner peripheralsurface 7A of the cylinder 7 and the piston 16 can be more securelyprevented from contacting each other.

Even though, in FIG. 8, the top end portion 22B1 of the lip ring 22 isshown having two bends, it may include, for example, three or fourbends. Increasing the number of bends included in the top end portion22B1, however, decreases the rigidity of the top end portion 22B1 toshorten the life of the lip ring 22, so that the number of bendsincluded in the top end portion 22B1 is preferably in a range of two tofour.

Third Embodiment

A reciprocating compressor according to a third embodiment of thepresent invention will be described below with reference to FIGS. 9 and10. Parts identical to those described above in connection with thefirst and second embodiments will be denoted by identical referencenumerals as used above and their description will be omitted.

In the third embodiment, the lip ring 22 has a curved portion, denotedas R1 in FIG. 9, on the inner peripheral surface between the bottomportion 22A and the side portion 22B. Compared with the firstembodiment, in the third embodiment with the curved portion R1 providedon the inner peripheral surface between the bottom portion 22A and theside portion 22B, the stress applied to the inner peripheral surfacebetween the bottom portion 22A and the side portion 22B where stressconcentration tends to occur is further reduced.

Also, as shown in FIG. 10, providing a curved portion R2 on the innerperipheral surface of the bent portion 22B3 included in the side portion22B of the lip ring 22 can further decrease, as compared with the firstembodiment, the stress applied to the inner peripheral surface of thebent portion 22B3 where stress concentration tends to occur.

The foregoing embodiments each represent a mere example of applicationof the present invention, and they do not define the technical scope ofthe present invention. The present invention can be applied in variousmanners without departing from the technical concept and main featuresthereof. The first to the third embodiments described above may also becombined in implementing the present invention.

What is claimed is:
 1. A reciprocating compressor, comprising: a pistonwhich compresses air by, while rocking, reciprocatingly moving in acylinder; and a sealing member which is fitted in a groove formed on thepiston for sealing between the cylinder and the piston, wherein thesealing member has a bottom portion to be fitted in the groove formed onthe piston and a side portion provided radially outwardly of the piston,and wherein the side portion includes a bent portion so as to reduce agap between an upper end portion thereof and the piston.
 2. Thereciprocating compressor according to claim 1, wherein an angle formedbetween a base end side of the side portion and the axial direction ofthe piston is larger than a rocking angle of the piston.
 3. Thereciprocating compressor according to claim 1, wherein the bottomportion of the sealing member is prevented from moving outwardly of thegroove formed on the piston.
 4. The reciprocating compressor accordingto claim 1, wherein the side portion includes a plurality of bends. 5.The reciprocating compressor according to claim 1, wherein the bentportion of the sealing member has a curved inner side surface.
 6. Thereciprocating compressor according to claim 1, wherein an inner sidesurface between the side portion and the bottom portion is curved.
 7. Areciprocating compressor comprising: a piston which compresses air by,while rocking, reciprocatingly moving in a cylinder; and a sealingmember which is fitted in a groove formed on the piston for sealingbetween the cylinder and the piston, wherein the sealing member has abottom portion to be fitted in the groove formed on the piston and aside portion provided radially outwardly of the piston, and wherein theside portion includes a plurality of bends causing a first angle formedbetween an upper end side of the side portion and the axial direction ofthe piston to be smaller than a second angle formed between a base endside of the side portion and the axial direction of the piston.
 8. Thereciprocating compressor according to claim 7, wherein the second angleformed between the base end side of the side portion and the axialdirection of the piston is larger than a rocking angle of the piston. 9.The reciprocating compressor according to claim 7, wherein the bottomportion of the sealing member is prevented from moving outwardly of thegroove formed on the piston.
 10. The reciprocating compressor accordingto claim 7, wherein the plurality of bends have a curved inner sidesurface.
 11. The reciprocating compressor according to claim 7, whereinan inner side surface between the side portion and the bottom portion iscurved.